Moisture-curable polyurethane coatings have been in use for a number of years. These coatings have been found to demonstrate superior wear characteristics when used on flooring products and, furthermore, they have demonstrated relatively good resistance to a variety of household staining agents. Nevertheless, such coatings have not proved to be satisfactory in all respects when used as floor coverings.
One method of preparing a durable flooring product is by forming a gelled, plasticized resilient substrate such as polyvinyl chloride, coating the substrate with a thin layer of moisture-curable urethane prepolymer, and then exposing the resulting material to heat and moisture to fuse the composite structure and cure the wear layer. Certain problems have been encountered with such structures, however. For example, the coating material is usually applied as a solvent solution which requires special handling. Further, plasticizer has tended to migrate from the substrate into the polyurethane wear layer, thus diminishing or altering the desirable characteristics of this layer. Accordingly, the flooring industry has investigated various ways to overcome these problems.